1. (1) water (2) ice (3) same speed in both (4) sound can only travel in a gas Do sound waves travel faster in water or in ice? ConcepTest 12.2a ConcepTest 12.2a Speed of Sound I

2. (1) water (2) ice (3) same speed in both (4) sound can only travel in a gas Do sound waves travel faster in water or in ice? ConcepTest 12.2a ConcepTest 12.2a Speed of Sound I inertia restoring force However, the force holding the molecules together is greater in ice (because it is a solid), so the restoring force is greater. v =  (force / inertia), greater in ice Speed of sound depends on the inertia of the medium and the restoring force. Since ice and water both consist of water molecules, the inertia is the same for both. However, the force holding the molecules together is greater in ice (because it is a solid), so the restoring force is greater. Since v =  (force / inertia), the speed of sound must be greater in ice !

3. Do you expect an echo to return to you more quickly or less quickly on a hot day, as compared to a cold day? 1) more quickly on a hot day 2) equal times on both days 3) more quickly on a cold day ConcepTest 12.2b ConcepTest 12.2b Speed of Sound II

4. Do you expect an echo to return to you more quickly or less quickly on a hot day, as compared to a cold day? 1) more quickly on a hot day 2) equal times on both days 3) more quickly on a cold day The speed of sound in a gas increases with temperature. This is because the molecules are bumping into each other faster and more often, so it is easier to propagate the compression wave (sound wave). ConcepTest 12.2b ConcepTest 12.2b Speed of Sound II

5. 1) about the same 2) about 10 times 3) about 100 times 4) about 1000 times 5) about 10,000 times A quiet radio has an intensity level of about 40 dB. Busy street traffic has a level of about 70 dB. How much greater is the intensity of the street traffic compared to the radio? ConcepTest 12.5b ConcepTest 12.5b Decibel Level II

6. increase by 10 dB  increase intensity by factor of 10 1 (10) increase by 20 dB  increase intensity by factor of 10 2 (100) increase by 30 dB  increase intensity by factor of 10 3 (1000) 1) about the same 2) about 10 times 3) about 100 times 4) about 1000 times 5) about 10,000 times A quiet radio has an intensity level of about 40 dB. Busy street traffic has a level of about 70 dB. How much greater is the intensity of the street traffic compared to the radio? ConcepTest 12.5b ConcepTest 12.5b Decibel Level II Follow-up: What decibel level gives an intensity a million times greater?

7. 1) the long pipe 2) the short pipe 3) both have the same frequency 4) depends on the speed of sound in the pipe You have a long pipe and a short pipe. Which one has the higher frequency? ConcepTest 12.6a ConcepTest 12.6a Pied Piper I

8. shorter pipe shorter wavelength frequency has to be higher A shorter pipe means that the standing wave in the pipe would have a shorter wavelength. Since the wave speed remains the same, the frequency has to be higher in the short pipe. 1) the long pipe 2) the short pipe 3) both have the same frequency 4) depends on the speed of sound in the pipe You have a long pipe and a short pipe. Which one has the higher frequency? ConcepTest 12.6a ConcepTest 12.6a Pied Piper I

9. If you blow across the opening of a partially filled soda bottle, you hear a tone. If you take a big sip of soda and then blow across the opening again, how will the frequency of the tone change? 1) frequency will increase 2) frequency will not change 3) frequency will decrease ConcepTest 12.6c ConcepTest 12.6c Pied Piper III

10. If you blow across the opening of a partially filled soda bottle, you hear a tone. If you take a big sip of soda and then blow across the opening again, how will the frequency of the tone change? 1) frequency will increase 2) frequency will not change 3) frequency will decrease longer pipe longer wavelength v = f frequency has to be lower By drinking some of the soda, you have effectively increased the length of the air column in the bottle. A longer pipe means that the standing wave in the bottle would have a longer wavelength. Since the wave speed remains the same, and since we know that v = f, then we see that the frequency has to be lower. ConcepTest 12.6c ConcepTest 12.6c Pied Piper III Follow-up: Why doesn’t the wave speed change?

11. 1) depends on the speed of sound in the pipe 2) you hear the same frequency 3) you hear a higher frequency 4) you hear a lower frequency You blow into an open pipe and produce a tone. What happens to the frequency of the tone if you close the end of the pipe and blow into it again? ConcepTest 12.7 ConcepTest 12.7 Open and Closed Pipes

12. open pipe1/2 of a wave closed pipe 1/4 of a wave wavelength is larger in the closed pipefrequency will be lower In the open pipe, 1/2 of a wave “fits” into the pipe, while in the closed pipe, only 1/4 of a wave fits. Because the wavelength is larger in the closed pipe, the frequency will be lower. 1) depends on the speed of sound in the pipe 2) you hear the same frequency 3) you hear a higher frequency 4) you hear a lower frequency You blow into an open pipe and produce a tone. What happens to the frequency of the tone if you close the end of the pipe and blow into it again? ConcepTest 12.7 ConcepTest 12.7 Open and Closed Pipes Follow-up: What would you have to do to the pipe to increase the frequency?

13. Pair 1Pair 2 1) pair 1 2) pair 2 3) same for both pairs 4) impossible to tell by just looking The traces below show beats that occur when two different pairs of waves interfere. For which case is the difference in frequency of the original waves greater? ConcepTest 12.10 ConcepTest 12.10 Beats

14. Pair 1Pair 2 difference in frequency f beat = f 2 – f 1 Recall that the beat frequency is the difference in frequency between the two waves: f beat = f 2 – f 1 greater beat frequency greater frequency difference Pair 1 has the greater beat frequency (more oscillations in same time period), so Pair 1 has the greater frequency difference. 1) pair 1 2) pair 2 3) same for both pairs 4) impossible to tell by just looking The traces below show beats that occur when two different pairs of waves interfere. For which case is the difference in frequency of the original waves greater? ConcepTest 12.10 ConcepTest 12.10 Beats

15. Observers A, B, and C listen to a moving source of sound. The location of the wave fronts of the moving source with respect to the observers is shown below. Which of the following is true? 1) frequency is highest at A 2) frequency is highest at B 3) frequency is highest at C 4) frequency is the same at all three points ConcepTest 12.11a ConcepTest 12.11a Doppler Effect I

16. Observers A, B, and C listen to a moving source of sound. The location of the wave fronts of the moving source with respect to the observers is shown below. Which of the following is true? 1) frequency is highest at A 2) frequency is highest at B 3) frequency is highest at C 4) frequency is the same at all three points observer C The number of wave fronts hitting observer C per unit time is greatest – thus the observed frequency is highest there. ConcepTest 12.11a ConcepTest 12.11a Doppler Effect I Follow-up: Where is the frequency lowest?

17. You are heading toward an island in a speedboat and you see your friend standing on the shore, at the base of a cliff. You sound the boat’s horn to alert your friend of your arrival. If the horn has a rest frequency of f 0, what frequency does your friend hear? 1) lower than f 0 2) equal to f 0 3) higher than f 0 ConcepTest 12.11b ConcepTest 12.11b Doppler Effect II

18. You are heading toward an island in a speedboat and you see your friend standing on the shore, at the base of a cliff. You sound the boat’s horn to alert your friend of your arrival. If the horn has a rest frequency of f 0, what frequency does your friend hear? 1) lower than f 0 2) equal to f 0 3) higher than f 0 approach of the source frequency is shifted higher Due to the approach of the source toward the stationary observer, the frequency is shifted higher. This is the same situation as depicted in the previous question. ConcepTest 12.11b ConcepTest 12.11b Doppler Effect II